The direction of a boat propellor is often controlled by a clutch control valve that controls the boat transmission. The clutch control valve is operated by a lever which, when moved in one direction, results in the propellor rotating in a direction that causes the boat to move forward and, when moved in an opposite direction, results in the propellor rotating in a drection that causes the boat to move in reverse. When the clutch lever is in a middle position, the clutch is engaged and the engine is in neutral.
A control system is usually employed to allow an operator to operate the clutch lever of an engine mounted below decks from the bridge of the boat. The control system usually comprises a control lever mounted in the bridge and means for transferring movement of the control lever to the clutch lever.
Several basic control systems are known that allow a remotely placed control lever to operate a clutch lever mounted on an engine. One such system is a cable based system that employs cables to transfer movement of the control lever to the clutch lever. An example of such a cable based system is shown in a sales brochure for the 2090 Series Two Station Lever Controls sold by Kobelt Manufacturing Co. Ltd of British Columbia, Canada. These cable based systems have been dissatisfactory because they are susceptible to corrosion caused by environmental factors. Further, the cables of such systems tend to stretch and therefore require frequent adjustment.
Hydraulic control systems have also employed to transfer movement of a control lever to that of a clutch lever. Hydraulic control systems employ master and slave pistons and a flowable working medium to transfer movement of the control lever to the clutch lever. These systems, while less susceptible to environmental factors than cable based systems, tend to suffer slow leaks where the piston shafts enter the cylinders. Over time, such leaks cause the master piston at the control lever come out of alignment, or synchronization, with the slave piston at the clutch lever. When the pistons of a hydraulic system are not synchronized as just-described, the control lever may indicate that the engine is in neutral when this is not the case. Should the pistons come out of synchronization, the hydraulic fluid must be removed from the system, the pistons adjusted, and the lines refilled. While systems for synchronizing hydraulic control systems are available, these synchronizing systems tend to be complex and expensive and are thus inappropriate for use with hydraulic systems for controlling marine transmissions where low cost and simplicity are required. Hydraulic control systems thus have not had great acceptance as control systems for marine transmissions.
It should be noted that the present invention is particularly useful when employed as a control system for controlling the transmission of a marine engine, and that application is described in detail herein. However, while the present invention is particularly effective when applied to such marine transmission control systems, the principles of the present invention may have application to other types of hydraulic control systems. The scope of the present invention is therefore to be determined by the attached claims and not the following detailed description.